Reference signal port discovery involving transmission points

ABSTRACT

A method includes receiving information indicating one or more sets of reference signal patterns from a first transmission point, wherein at least one of the indicated one or more sets of reference signal patterns corresponds to one of one or more other transmission points; measuring the channel quality for the indicated sets of reference signal patterns; and reporting indications of the measured channel quality for the indicated one or more sets of reference signal patterns to the first transmission point. Another method includes transmitting information indicating one or more sets of reference signal patterns from a first transmission point to a user equipment, wherein at least one of the indicated one or more sets of reference signal patterns corresponds to one of one or more other transmission points; and receiving from the user equipment indications of measured channel quality for the indicated one or more sets of reference signal patterns.

TECHNICAL FIELD

This invention relates generally to radio frequency communications and,more specifically, relates to mobility of a wireless device.

BACKGROUND

This section is intended to provide a background or context to theinvention that is recited in the claims. The description herein mayinclude concepts that could be pursued, but are not necessarily onesthat have been previously conceived or pursued. Therefore, unlessotherwise indicated herein, what is described in this section is notprior art to the description and claims in this application and is notadmitted to be prior art by inclusion in this section.

The following abbreviations that may be found in the specificationand/or the drawing figures are defined as follows:

-   -   3GPP third generation partnership project    -   BS base station    -   COMP coordinated multipoint    -   CSI channel state information    -   CSI-RS channel state information reference signals    -   CQI channel quality indicator    -   DL downlink (from base station to user equipment)    -   DM-RS demodulation reference symbols    -   eNB E-UTRAN Node B (evolved Node B, also eNodeB)    -   E-UTRAN evolved UTRAN (LTE)    -   LTE long term evolution of UTRAN (E-UTRAN)    -   LTE-A LTE advanced    -   MCS modulation and coding scheme    -   MIMO multiple input multiple output    -   MME mobility management entity    -   NCE network control element    -   PDSCH physical downlink shared channel    -   PMI precoding matrix indicator    -   PUCCH physical uplink control channel    -   PUSCH physical uplink shared channel    -   OFDM orthogonal frequency division multiplexing    -   OFDMA orthogonal frequency division multiple access    -   Rel. release    -   TM transmission mode    -   TS technical standard    -   RAT radio access technology    -   RRH remote radio head    -   RS reference signal/symbol    -   RSRP reference symbol received power    -   RSRP reference symbol received quality    -   SC-FDMA single carrier, frequency division multiple access    -   SGW serving gateway    -   SRS sounding reference symbols    -   UE user equipment, such as a mobile station, mobile node or        mobile terminal    -   UL uplink (from user equipment to base station)    -   UTRAN universal terrestrial radio access network    -   WCDMA wideband code division multiple access

COordinated MultiPoint (COMP) transmission and reception is one of theinvestigated technologies in 3GPP LTE-A to enhance specifically thecell-edge data rates in order to create a more uniform data rateexperience for the end user over the entire cell area. The COMPtechniques involve increased collaboration between differenttransmission/reception points (e.g., eNodeBs, RRHs, hotspots, homeeNodeBs etc.) in DL transmissions to the UE and UT receptions from theUE.

Already in Rel. 10, there has been a related study item in 3GPP, but thestudy item had been put on hold. The study item was recently restartedin 3GPP in January 2011 according to the study item description.Moreover, different scenarios to be investigated have been agreed to in3GPP for the study item phase. One of the agreed scenarios (RAN1#63bismeeting, Dublin, January 2011) concentrates on a network with low powerRRHs within the macro cell coverage where the transmission/receptionpoints created by the RRHs have the same cell IDs as the macro cell.This situation is denoted therein as “single-cell COMP”.

BRIEF SUMMARY

An exemplary method includes receiving information indicating one ormore sets of reference signal patterns from a first transmission point,wherein at least one of the indicated one or more sets of referencesignal patterns corresponds to one of one or more other transmissionpoints; measuring the channel quality for the indicated one or more setsof reference signal patterns; and reporting indications of the measuredchannel quality for the indicated one or more sets of reference signalpatterns to the first transmission point.

An exemplary apparatus includes one or more processors and one or morememories including computer program code. The one or more memories andthe computer program code are configured to, with the one or moreprocessors, cause the apparatus to perform at least the following:receiving information indicating one or more sets of reference signalpatterns from a first transmission point, wherein at least one of theindicated one or more sets of reference signal patterns corresponds toone of one or more other transmission points; measuring the channelquality for the indicated one or more sets of reference signal patterns;and reporting indications of the measured channel quality for theindicated one or more sets of reference signal patterns to the firsttransmission point

In an additional exemplary embodiment, a computer program productincludes a computer-readable memory bearing computer program codeembodied therein for use with a computer. The computer program codeincludes: code for receiving information indicating one or more sets ofreference signal patterns from a first transmission point, wherein atleast one of the indicated one or more sets or reference signal patternscorresponds to one of one or more other transmission points; code formeasuring the channel quality for the indicated one or more sets ofreference signal patterns; and code for reporting indications of themeasured channel quality for the indicated one or more sets of referencesignal patterns to the first transmission point.

Another exemplary method includes transmitting information indicatingone or more sets of reference signal patterns from a first transmissionpoint to a user equipment, wherein at least one of the indicated one ormore sets of reference signal patterns corresponds to one of one or moreother transmission points; and receiving from the user equipmentindications of measured channel quality for the indicated one or moresets of reference signal patterns.

A further exemplary embodiment includes an apparatus that includes oneor more processors one or more memories including computer program code.The one or more memories and the computer program code are configuredto, with the one or more processors, cause the apparatus to perform atleast the following: transmitting information indicating one or moresets of reference signal patterns from a first transmission point to auser equipment, wherein at least one of the indicated one or more setsof reference signal patterns corresponds to one of one or more othertransmission points; and receiving from the user equipment indicationsof measured channel quality for the indicated one or more sets ofreference signal patterns.

In an additional exemplary embodiment, a computer program productincludes a computer-readable memory bearing computer program codeembodied therein for use with a computer. The computer program codeincludes code for transmitting information indicating one or more setsof reference signal patterns from a first transmission point to a userequipment, wherein at least one of the indicated one or more sets ofreference signal patterns corresponds to one of one or more othertransmission points; and code for receiving from the user equipmentindications of measured channel quality for the indicated one or moresets of reference signal patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of embodiments of this invention aremade more evident in the following Detailed Description of ExemplaryEmbodiments, when read in conjunction with the attached Drawing Figures,wherein:

FIG. 1 shows a simplified block diagram of various electronic devicesthat are suitable for use in practicing the exemplary embodiments ofthis invention.

FIG. 2 reproduces FIG. 4 of 3GPP TS 36,300 and shows the overallarchitecture of the EUTRAN system, and illustrates an exemplaryembodiment where the base station of FIG. 1 is embodied as an eNB in anLTE or an LTE-A of wireless communication system.

FIG. 3 is a diagram us rating a procedure of data transmission usingCSI-RS.

FIG. 4 is an example of a macro cell having multiple transmission pointswithin the macro cell.

FIG. 5 is an example of a CSI-RS muting pattern combined with theUE-specifically configured CSI-RS ports and the channel and signalquality measured and reported by a user equipment.

FIG. 6 is an example of a CSI-RS muting pattern combined with theUE-specifically configured CSI-RS ports and the channel and signalquality measured and reported by a user equipment.

FIG. 7 shows an example of how the CSI-RS muting pattern is mapped tocorresponding resource elements in a resource space.

FIG. 8 is a signaling diagram illustrating an exemplary procedure formeasuring, determining and signaling the CSI-RS antenna ports to beconfigured.

FIG. 9 is a block diagram of an exemplary method performed by a userequipment for reference signal port discovery involving transmissionpoints.

FIG. 10 is a block diagram of an exemplary method performed by atransmission point in a cell for reference signal port discoveryinvolving other transmission points in the cell.

DETAILED DESCRIPTION OF THE DRAWINGS

Before describing in further detail the exemplary embodiments of thisinvention, reference is made to FIG. 1 for illustrating a simplifiedblock diagram of various apparatus that are suitable for use inpracticing the exemplary embodiments of this invention. In FIG. 1, awireless network 90 includes an eNB 12, an NCE/MME/SGW 14, and atransmission point such as RRH 130. The wireless network 90 is adaptedfor communication over a wireless link 35 with an apparatus, such as amobile communication device which may be referred to as a LIE 10, via anetwork access node, such as a Node B (base station), and morespecifically an eNB 12. The network 90 may include a network controlelement (NCE) 14 that may include MME/SOW functionality, and whichprovides connectivity with a further network, such as a telephonenetwork and/or a data communications network 85 (e.g., the internet)through link 25. The NCE 14 includes a controller, such as at least onecomputer or a data processor (DP) 14A, and at least one non-transitorycomputer-readable memory medium embodied as a memory (MEM) 14B thatstores a program of computer instructions (PROG) 10C.

The UE 10 includes a controller, such as at least one computer or a dataprocessor (DP) 10A, at least one non-transitory computer-readable memorymedium embodied as a memory (MEM) 10B that stores a program of computerinstructions (PROG) 10C, and at least one suitable radio frequency (RE)transceiver 10D for bidirectional wireless communications with the eNB12 via one or more antennas 10E. The eNB 12 also includes a controller,such as at least one computer or a data processor (DP) 12A, at least onecomputer-readable memory medium embodied as a memory (MEM) 12B thatstores a program of computer instructions (PROG) 12C, and at least onesuitable RF transceiver 12D for communication with the UE 10 via one ormore antennas 12E (typically several when multiple input, multipleoutput (MIMO) operation is in use). The eNB 12 is coupled via a data andcontrol path 13 to the NCE 14. The path 13 may be implemented as an S1interface. The eNB 12 may also be coupled to another transmission pointvia data and control path 15, which may be implemented as an X2interface in case of another logical base station or can be a directeNodeB internal interface, e.g., optical fiber connection, to connectsome transmission point such as radio remote head (RRH) 130 to the eNB12. Typically, the eNB 12 covers a single macro cell (shown in FIG. 4)via the one or more antennas 12E.

In this example, the transmission point 130 includes a controller, suchas at least one computer or a data processor (DP) 130A, at least onecomputer-readable memory medium embodied as a memory (MEM) 130B thatstores a program of computer instructions (PROG) 130C, and at least onesuitable RF transceiver 130D for communication with the UE 10 via one ormore antennas 130E (as stated above, typically several when multipleinput, multiple output (MIMO) operation is in use). The transmissionpoint 130 communicates with the UE 10 via a link 36. The transmissionpoint 130 may communicate, depending on implementation, with the eNB 12using a data and control path 15. The transmission point 130 can beanother eNodeB or can be logically be part of eNB 12 as, e.g., enabledby a Radio Remote Head (RRH) and creates some local hotspot coverage 410inside the macro cell coverage area (as shown in FIG. 4). Forsingle-cell MIMO—all of the transmission points 130 (see also FIG. 4)are under full control of a single eNB 12. Thus, there is centrally someunit where several transmission points/RRHs 130 are connected as such.The idea is that the transmission points 130 and the macro eNB 12 arecentrally controlled together. The control is typically at the locationof the macro eNB 12, but could also be at a location that is connectedto the eNB 12 and the transmission point 130.

At least one of the PROGs 10C, 12C, and 130C is assumed to includeprogram instructions that, when executed by the associated DP, enablethe corresponding apparatus to operate in accordance with the exemplaryembodiments of this invention, as will be discussed below in greaterdetail. That is, the exemplary embodiments of this invention may beimplemented at least in part by computer software executable by the DP10A of the UE 10 and/or by the DP 12A of the eNB 12, and/or by the DP130A of the base station 120, or by hardware (e.g., an integratedcircuit configured to perform one or more of the operations describedherein), or by a combination of software and hardware (and firmware).

In general, the various embodiments of the UE 10 can include, but arenot limited to, cellular telephones, tablets having wireless capability,personal digital assistants (PDAs) having wireless communicationcapabilities, portable computers having wireless communicationcapabilities, image capture devices such as digital cameras havingwireless communication capabilities, gaming devices having wirelesscommunication capabilities, music storage and playback appliances havingwireless communication capabilities, Internet appliances permittingwireless Internet access and browsing, as well as portable units orterminals that incorporate combinations of such functions.

The computer-readable memories 10B, 12B, and 130B may be of any typesuitable to the local technical environment and may be implemented usingany suitable data storage technology, such as semiconductor based memorydevices, random access memory, read only memory, programmable read onlymemory, flash memory, magnetic memory devices and systems, opticalmemory devices and systems, fixed memory and removable memory. The dataprocessors 10A, 12A, and 130A may be of any type suitable to the localtechnical environment, and may include one or more of general purposecomputers, special purpose computers, microprocessors, digital signalprocessors (DSPs) and processors based on multi-core processorarchitectures, as non-limiting examples.

In one non-limiting embodiment, the BS 12 can be embodied as an eNB ifthe wireless network 1 is a long term evolution (LTE) or an LTE-Advanced(LTE-A) E-UTRAN type of network. FIG. 2 shows the overall architectureof the E-UTRAN system. The network 90 includes a core network thatincludes at least one serving gateway (SG-W in FIG. 2 and SGW in FIG. 1)and can include at least one a mobility management entity (MME), herecollectively shown as the MME/S-GW. In this system, the DL accesstechnique is OFDMA, and the UL access technique is SC-FDMA.

Now that exemplary apparatus have been described, additional detail onthe exemplary embodiments of the invention is described. Exemplaryembodiments of the instant invention relate to DL COMP operation ingeneral, but specifically also to the envisioned single-cell operationmode (“single-cell COMP”) of coordinated multipoint reception andtransmission, which was described above.

In LTE Release-10, one of the main new features is the introduction ofCSI-RS (channel state information-reference signals). The idea is totransmit separate cell specific (common) RS for CSI estimation purposesin some selected subframes with, e.g., 10 ms (millisecond) periodicity.Turning to FIG. 3, a diagram is shown that illustrates a procedure ofdata transmission using CSI-RS. The UE estimates the CSI (“CSImeasurement”) based upon the CSI-RS transmitted by the eNodeB andtransmits the CSI feedback (“CSI report”) to the eNodeB, which in turncan use the CSI in the selection of the precoder for the data. Inreference 3, the data is transmitted together with user specific (i.e.,dedicated) demodulation reference symbols (DM-RS), spanning the samephysical resource blocks as the data. The same precoding is applied forthe DM-RS and the data. This allows for the usage of any precoding bythe eNodeB, as the precoding applied remains transparent to the userequipment and does not need to be signaled to the user equipment.

In addition to the CSI-RS transmission for one cell (e.g. a macro cell),the LTE Rel-10 also provides a possibility to configure other CSI-RSpatterns (e.g., sets of resource elements) with zero transmit power.This is described below in more detail in reference to FIG. 7. Thesepatterns are signaled to user equipment via muting patterns, and theseindicate which of the resource elements the eNodeB will leave empty whentransmitting data on PDSCH. This allows for a potentially future proofCSI-RS design, so that a Rel. 11 UE can, e.g. measure CSI-RS frommultiple cells simultaneously without PDSCH interference (a feature notyet included into LTE Rel-10).

One example of a network deployment scenario of interest in this case isdepicted in FIG. 4. Within the coverage area 400 of one macro eNodeB 12with, e.g., 4 TX antennas 12E, there are altogether four hotspots 410-1through 410-4 created by four transmission points 130-1 through 130-4,each having some (1, 2, 4 or 8) transmit antennas 130E and a respectivenumber (1, 2, 4 or 8) of CSI-RS antenna ports.

The transmission points 130 may or may not have the same cell ID(identity) as the macro transmission point 12:

-   -   In the conventional heterogeneous networks scenario, the        transmission points 130 are cells of their own, each having a        distinct cell ID.    -   In case of single-cell COMP, several transmission points/nodes        such as the transmission points 130 implemented, e.g., through        Remote Radio Heads (RRHs) as well as the macro eNodeB 12,        possibly having different transmission powers, share the same        physical cell-1D and are only to be distinguished by the UE by        different CSI-RS.

In both of the above mentioned scenarios, constantly monitoring andreporting the channel state information (CSI) for all the CSI-RS antennaports configured for all transmission points/nodes would dramaticallyincrease the measurement overhead and reporting overhead for the UE andtherefore, from a network point of view, the UL control channeloverhead. It is therefore of advantage that the UE would only regularlyreport the CSI for the macro eNodeB 12 and the transmission points 130which, e.g., are closest to the user equipment or have best signalquality, and utilize only this subset of transmission points in the CSIreporting and related DL COMP operations (which is called in the 3GPPcommunity the “DL COMP collaboration set”) for the user equipment.

One exemplary problem therefore is how the eNodeB/network and the UEdetermine which of the transmission points (eNB 12 and transmissionpoints 130) out of a set of configured CSI-RS antenna ports should beincluded in the regular CSI and channel quality (CQI) reporting and theDL COMP operations. An issue to be solved, consequently, is how thenetwork/eNodeBs and the UE “know” and define the CSI-RS antenna portsthe UE is supposed to regularly monitor, create CSI measurements basedon, and report back to the network.

The instant invention proposes a solution to this problem, based in anexemplary embodiment on the available CSI-RS antenna port information atthe UE. An exemplary embodiment utilizes the “zero power CSI-RS bitmap”,also called the CSI-RS muting pattern in this disclosure, as well as theUE-specific configured reference signal ports at the LTE. Regarding thezero power CSI-RS pattern, see section 6.10.5 in 3GPP TS 36,211, drafta00 for version 10.0.0, December 2010. The CSI-RS muting pattern mayindicate the CSI-RS patterns that are configured within the area ofinterest (multiple transmission points (RRHs) 130 with the same cell IDand/or a few neighboring cells; see FIG. 4). This muting patternincludes 16 bits, so that the use equipment knows what modulationsymbols in addition to the configured UE-specific CSI-RS ports have tobe rate-matched from the PDSCH in the PDSCH decoding process whenutilizing 3GPP LTE DL transmission mode 9 (TM9), which is based on theutilization of CSI-RS for channel state information and DM-RS fordecoding the received data. Each of the bits in the muting patternindicates four resource elements for up to four CSI-RS antenna portsconfigured within the area.

It is helpful at this point to provide a simple example. Assume (asshown in FIG. 4) there is one macro cell 400 and four hotspots 410-1 to410-4, created by corresponding transmission points A 130-1 to D 130-4.Assume the UE is connected to the macro cell 400/eNB 12 and isconfigured initially to use the CSI-RS antenna ports of the macro cell(see CSI-RS configuration number (#) 5 in FIGS. 5 and 6) and eachtransmission point 130 is assigned one CSI-RS configuration, resultingin a corresponding muting pattern for the UE. In the example shown inFIGS. 5 and 6, CSI-RS antenna ports of transmission point (T.P.) A 130-1result in an entry in number two of the muting pattern, transmissionpoint B 130-2 in number three, transmission point C 130-3 in number 7,and transmission point D 130-4 in number 9 of FIG. 5. Although not shownin FIGS. 5 and 6, the respective configurations may also includepossible muting pattern entries of neighboring cells/eNodeBs that aresignaled to the UE 10 of interest using the CSI-RS muting pattern 510(shown in FIGS. 5 and 6).

An exemplary technique is to utilize the information contained in theCSI-RS muting pattern 510 about the possible number of configured CSI-RSantenna ports available for DL COMP cooperation and their position inthe time-frequency domain within the PDSCH area of the LTE DL subframe(see FIG. 7) and request the UE to measure the channel quality (e.g.,signal-strength) of all the CSI-RS antenna port groups indicated by theCSI-RS muting pattern 510 in addition to the for the UE configuredCSI-RS patterns. For instance, in the present example, the UE is able todetect the CSI-RS from the transmission points B 130-2, C 130-3, and D130-4, as indicated in FIGS. 5 and 6 and also the CSI-RS configured forthe UE 10 (e.g., from the macro cell 400, as indicated by the configuredUE-specific CSI-RS report 515). It is noted that zeros may be usedinstead of ones to indicate which CSI-RS antenna ports are active.

It is noted that FIG. 7 shows an example of how the CSI-RS mutingpattern 510 is mapped to a zero power CSI-RS configuration (indicated bynumbered resource elements) in the resource space 700. The resourcespace 700 in this example is a PDSCH area of an LTE DL subframe. Eachbit 710 in the CSI-RS muting pattern 510 corresponds to a set 720 offour resource elements 730-1, 730-2, 730-3, 730-4 in the resource space700. A resource element 730 is an OFDM symbol occurring at a particulartime and on a particular subcarrier. See, e.g., 3GPP TS 36.211 version10.0.0 (December 2010), Chapter 6 and in particular 6.2.2 for adescription of the PDSCH area of an LTE DL subframe. The main purpose ofthe zero power CSI-RS configuration is to avoid CSI-RS interferencebetween neighbor cells. The zero power CSI-RS configuration alsoprovides accurate inter-cell CSI measurement and guarantees future CoMPperformance. The zero power CSI-RS configuration is independent fromthat of CSI-RS with its own duty-cycle and offset. Muting is alwaysfull-band configured for all PRBs (physical resource blocks). The 16bits 710 are used to indicate which resource elements should be muted,and cover both common and TDD only patterns. Each bit corresponds to,e.g., four resource elements following a 4Tx antenna port CSI-RSpattern. That is, the CSI-RS configuration for a cell or a transmissionpoint (macro or hotspot) can require 2, 4, or 8 REs, depending on thenumber of antennas. For four antennas, four REs are needed. Since everybit in the muting pattern corresponds to four REs, this was designedsuch that these four REs correspond to a possible configuration of 4TxCSI-RS in a neighboring cell or a transmission point belonging to thesame logical cell. If two bits are “on” in the muting pattern, these canmatch two different 4Tx CSI-RS configurations in neighboring cells ortransmission points) or they can match one 8Tx CSI-RS configuration in aneighboring cell/transmission point. In the example shown in FIG. 7, bit710-3 corresponds to a set 720 having resource elements 730-1, 730-2,730-3, and 730-4 in the positions shown. It is noted that a set 720 maycontain other numbers of resource elements.

That is, the UE 10 in FIG. 4 determines, using the CSR-RS muting pattern510 as well as the UE-specific configured CSI-RS ports 515, which set720 of resource elements 730 should be used to measure channel qualityfrom other transmission points. Transmission point A 130-1 is configuredto transmit its CSI reference signals on two reference symbols withinthe four resource elements 730-1 through 730-4. The other transmissionpoints B 103-2. C 130-3, and D 130-4 are also similarly configured totransmit CSI reference signals at their respective sets 720 of resourceelements 730, as indicated in FIG. 7. The UE 10 performs channel qualitymeasurements of these sets 720 of resource elements including also forthe LIE configured CSI-RS antenna ports 515 (e.g., from the macro cell400).

The report 520 is then sent by the UE 10 to the eNodeB. The granularityof the report 520-1 may be the same as in the muting bitmap, i.e. groupsof four CSI-RS antenna ports as shown in FIG. 5. Alternatively, thereport 520-2 could be based on a CSI-RS antenna port level granularityas is the case in FIG. 6. Based on the report 520, the eNodeB is awareof the signal strength of the CSI-RS antenna port groups and istherefore able to configure the UE to utilize the best subset of CSI-RSantenna ports (e.g., a maximum of eight antenna ports out of thecombined antenna ports of the macro eNodeB cell and the othertransmission points) in a UE specific manner for the further COMP ornormal Rel. 10 TM9 operation.

The COMP collaboration set definition can be considered to be of thefollowing exemplary operations, as shown in FIG. 8:

1. The eNodeB signals the CSI-RS muting pattern 510 as well as theUE-specific CSI-RS configuration 515 to the UE.

2. The eNodeB requests a report from the UE about the channel quality ofthe different sets of CSI-RS patterns (corresponding to sets 720indicated by the CSI-RS muting pattern 510) and the configuredUE-specific CSI-RS antenna ports 515 (e.g., from the macro cell in caseof initial COMP collaboration-set search).

3. The UE checks the channel quality of the individual CSI-RS patternsets (each set comprising four CSI-RS patterns/ports as indicated by theCSI-RS muting pattern 510 and the configured UE-specific CSI-RS antennaports 515 as shown in FIG. 7).

a. The definition of channel quality in this context may comprise forinstance the following:

i. Average received CSI-RS power over the patterns/ports within thereporting granularity (e.g., one or four CSI-RS antenna ports) oralternatively, of the strongest best pattern within the reportinggranularity set.

ii. Average received SINR (signal to interference plus noise ratio) overthe patterns ports within the reporting granularity or alternatively, ofthe strongest/best pattern within the reporting granularity set.

iii. The projected data throughput assuming the respective antenna portswithin the reporting granularity were used in PDSCH data transmission(i.e., similar to the CQI definition in LTE). Alternatively, only thestrongest antenna port within the reporting granularity might beconsidered.

4. The UE reports the outcome of the measurement to the eNodeB. Thereporting may be implemented using, e.g., layer 1 (L1) signaling similarto the CSI measurements, or via MAC (media access control) procedures asis the case with, e.g., RSRP/RSRQ measurements in LTE Differentreporting granularities and information might be considered for report520):

a. A bitmap of the best CSI-RS pattern sets is reported back to theeNodeB (e.g., a subset of the CSI-RS patterns as indicated by the mutingpattern and the UE-specific configured CSI-RS antenna ports). Thisinformation gives only the identity for the CSI-RS pattern within thereporting granularity but not quality of individual CSI-RS pattern orpattern set.

b. Indication of the sets of CSI-RS patterns together with the relativechannel quality compared to the strongest/best sets of CSI-RS patterns.For example, the UE may send an indication of the strongest/best sets ofCSI-RS patterns with four bits (one out of 16 sets), and for each set ofweaker CSI-RS patterns, the UE indicates a relative performance/qualitycompared to that of the strongest set. The UE may also indicate theperformance/quality corresponding to the strongest set of CSI-RSpatterns. This reporting requires higher signaling overhead, butprovides better, more elaborate information to the eNodeB in theselection of the COMP collaboration set for each specific UE.

The eNodeB might provide certain measurement restrictions to the UE inorder to guide the UE on how to construct the final report 520:

i. The selection can be based on the N strongest/best sets of CSI-RSpatterns depending on the related reporting granularity. The value of Ncould be set by the eNodeB by higher layer signaling. Thus, a UE willreport exactly the N strongest/best set of CSI-RS patterns.

ii. The eNodeB guides the UE to take into account a relativequality/performance measure compared to the best quality/performanceCSI-RS patterns. The UE therefore only reports the sets of CSI-RSpatterns (depending again on the reporting granularity) fulfilling thisrequirement (e.g., number of reported sets of CSI-RS patterns dependingon that quality/performance difference).

iii. The eNodeB could also request the UE to either report according toreport (a) above (e.g., just indicating the better of the available setsof CSI-RS patterns) or request a better reporting as described above.

5. The eNodeB receives the report 520 from the UE and determines a UEspecific COMP collaboration set meaning, the eNodeB decides which CSI-RSantenna ports the transmission point assigns to each specific UE to bemonitored and CSI information to be provided by the UE for DL operationin TM9 (including single-cell COMP).

6. The eNodeB informs the UE about the updated CSI-RS antenna ports theUE should be accordingly monitoring and should base the operation of theUE on, and also the CSI information to be provided by the UE. Typically,the CSI-RS antenna ports would be limited to the specific ports the UEis able to receive.

7. The UE performs channel quality measurements based on the UE specificCSI-RS configuration according to normal CSI-RS based DL operation ofe.g. LTE.

Note that the eNodeB could trigger the report request in (2) to (4)regularly, in order to keep the longer-term track of the best possibleCOMP collaboration set for single-cell ID COMP operations.

Turning to FIG. 9, a block diagram is shown of an exemplary methodperformed by a user equipment for reference signal port discoveryinvolving, multiple transmission points. In the examples of FIGS. 9 and10, the first transmission point is the eNodeB 12. However, it might bepossible for other transmission points in a cell to perform theseoperations. In block 905, the user equipment receives an indication of aUE specific reference signal pattern to be measured from a firsttransmission point in a cell. In block 910, the user equipment receivesinformation from the first transmission point in the cell. Theinformation indicates sets of reference signal patterns and which setsof reference signal patterns have zero transmission power (e.g., asindicated by the CSI-RS muting pattern) for certain frames of DLtransmissions by the first transmission point. The full set of referencesignal patterns may correspond to one of one or more other transmissionpoints in the cell or a neighboring cell.

The user equipment may or may not use the CSI-RS muting pattern forchannel quality measurements. If the user equipment should use theCSI-RS muting pattern for performing channel quality measurements, thenthe user equipment should be informed of such. There are multipleoptions for this to occur.

For example, in block 915, the user equipment optionally receivessignaling from first transmission point of channel quality informationto be reported by the user equipment to the first transmission point.That is, the first transmission point indicates which of the scenariosin step 4 above are to be used to report the channel quality. Anotheroption is illustrated by block 916, where the user equipment receivessignaling from the first transmission point to perform channel qualitymeasurements using the information (e.g., the CSI-RS muting pattern).Yet another option is illustrated by block 917, where the user equipmentis configured (e.g., with original or updated software) to alwaysperform channel quality measurements using the information (e.g., theCSI-RS muting pattern).

Thus, in block 919, the user equipment determines if the user equipmentshould use the indicated sets of reference signal patterns formeasurements of channel quality. If not (block 919=NO), the userequipment measures and reports (block 919) channel quality for the userequipment specific reference signal pattern received in block 905.

In block 920 (performed if block 919=YES), based on the receivedinformation, the user equipment measures the channel quality for theindicated sets of reference signal patterns (received in block 910) andfor the UE specific reference signal pattern (received in block 905).

In block 930, the user equipment reports indications of the measuredchannel quality for the indicated sets of reference signal patterns andfor the UE specific reference signal pattern to the first transmissionpoint. It is noted that the UE specific reference signal pattern couldbe transmitted separately. These indications are in accordance with thesignals received in block 915. In block 940, the user equipment receivessignaling of indications of an updated user equipment specific group ofCSI-RS patterns the user equipment should measure and of channel qualityinformation to be sent to the first transmission point.

In FIG. 10, a block diagram is shown of an exemplary method performed bya first transmission point (such as eNodeB 12) in a cell for referencesignal port discovery involving several transmission points within thecell. In block 1005, the first transmission point transmits anindication of a UE specific reference signal pattern to UE. In block1010, the first transmission point transmits information to a userequipment in a cell. The information indicates sets of reference signalpatterns that have zero transmission power (e.g., as indicated by theCSI-RS muting pattern) for certain frames of DL transmissions by thefirst transmission point. The full set of thereby indicated referencesignal patterns may correspond to one of one or more other transmissionpoints in the cell or neighboring cells.

In block 1011, the transmission point determines if the user equipmentshould use the indicated sets of reference signal patterns formeasurement of channel quality. If not (block 1011=NO), in block 1019,the transmission point receives from the user equipment a report ofchannel quality for the user equipment specific reference signal pattern(corresponding to block 1005). If so (block 1011=YES), the transmissionpoint selects one of the blocks 1015, 1016, or 1017.

The transmission point, in block 1015, determines channel qualityinformation to be provided by the user equipment (see, e.g., step 4above in reference to FIG. 8) and signals this information to the userequipment. In block 1016, the transmission point determines that theuser equipment is already configured to always perform channel qualitymeasurements using the transmitted information in block 1010, and thetransmission point takes no action.

In block 1020, the transmission point receives from the user equipmentindications of the measured channel quality for the indicated sets ofreference signal patterns and typically also the UE specific referencesignal pattern. The transmission point, in block 1030, determines anupdated user equipment specific group of CSI-RS patterns for the UE. Inblock 1050, the transmission point signals indications of the determinedupdated user equipment specific group of sets of CSI-RS patterns.

Without in any way limiting the scope, interpretation, or application ofthe claims appearing below, a technical effect of one or more of theexample embodiments disclosed herein is use of information, such as apattern like the CSI-RS pattern, to indicate to a user equipment whichsets of CSI-RS patterns should have its channel quality measured andhaving the user equipment inform a transmission point as to the resultsof the channel quality measurements.

Embodiments of the present invention may be implemented in software,hardware, application logic or a combination of software, hardware andapplication logic. In an example embodiment, the application logic,software or an instruction set is maintained on any one of variousconventional computer-readable media. In the context of this document, a“computer-readable medium” may be any media or means that can contain,store, communicate, propagate or transport the instructions for use byor in connection with an instruction execution system, apparatus, ordevice, such as a computer, with one example of a computer described anddepicted, e.g., in FIG. 1. A computer-readable medium may comprise acomputer-readable storage medium that may be any media or means that cancontain or store the instructions for use by or in connection with aninstruction execution system, apparatus, or device, such as a computer.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the above-described functions may be optional ormay be combined.

Although various aspects of the invention are set out in the independentclaims, other aspects of the invention comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

It is also noted herein that while the above describes exampleembodiments of the invention, these descriptions should not be viewed ina limiting sense. Rather, there are several variations and modificationswhich may be made without departing from the scope of the presentinvention as defined in the appended claims

1-54. (canceled)
 55. A method comprising: receiving informationindicating one or more sets of reference signal patterns from a firsttransmission point, wherein the one or more sets of reference signalpatterns comprise one or more muting reference signal patterns that havezero transmit power for certain frames of transmissions by the firsttransmission point; measuring the channel quality for the indicated oneor more sets of reference signal patterns using the one or more mutingreference signal patterns; and reporting indications of the measuredchannel quality for the indicated one or more sets of reference signalpatterns to the first transmission point.
 56. The method of claim 55,wherein the information comprises a pattern of bits, each of the bitsindicating a set of reference signal patterns that should be measuredfor channel quality.
 57. The method of claim 56, wherein the patterncomprises a zero power channel state information-reference signalbitmap.
 58. The method of claim 55, further comprising: receiving anindication of a user equipment specific reference signal pattern thatshould be measured for channel quality; and wherein measuring furthercomprises measuring the user equipment specific reference signal patternfor channel quality; and reporting further comprises reporting both themeasured channel quality for the indicated one or more sets of referencesignal patterns and for the user equipment specific reference signalpattern.
 59. The method of claim 55, wherein reporting indications ofthe measured channel quality further comprises reporting for at leastone of the indicated one or more sets of reference signal patternswhether a corresponding measured channel quality meets a predeterminedthreshold.
 60. The method of claim 55, wherein: measuring furthercomprises measuring, for at least one of the indicated one or more setsof reference signal patterns, channel quality for a plurality of ports;and reporting further comprises reporting for the at least one of theindicated one or more sets of reference signal patterns and acorresponding plurality of ports whether a corresponding measuredchannel quality meets a predetermined threshold.
 61. The method of claim55, wherein the measuring is performed in response to a channel stateinformation-reference signals report request message.
 62. The method ofclaim 55, wherein the reporting is performed using a channel stateinformation-reference signals quality report message.
 63. The method ofclaim 55, wherein: the first transmission point is in a cell; the one ormore other transmission points are a plurality of other transmissionpoints; at least one of the plurality of other transmission points is inthe cell; and at least an additional one of the plurality of othertransmission points are in one or more neighbor cells.
 64. The method ofclaim 55, wherein measuring the channel quality is performed in responseto signaling from the first transmission point indicating the indicatedone or more sets of reference signal patterns are to be measured forsignal quality.
 65. The method of claim 55, wherein measuring thechannel quality is performed in response to signaling from the firsttransmission point indicating the indicated one or more sets ofreference signal patterns are to be measured for signal quality.
 66. Anapparatus comprising: one or more processors; and one or more memoriesincluding computer program code, the one or more memories and thecomputer program code configured, with the one or more processors, tocause the apparatus to perform at least the following: receivinginformation indicating one or more sets of reference signal patternsfrom a first transmission point, wherein the one or more sets ofreference signal patterns comprise one or more muting reference signalpatterns that have zero transmit power for certain frames oftransmissions by the first transmission point; measuring the channelquality for the indicated one or more sets of reference signal patternsusing the one or more muting reference signal patterns; and reportingindications of the measured channel quality for the indicated one ormore sets of reference signal patterns to the first transmission point.67. The apparatus of claim 66, wherein the information comprises apattern of bits, each of the bits indicating a set of reference signalpatterns that should be measured for channel quality.
 68. The apparatusof claim 67, wherein the pattern comprises a zero power channel stateinformation-reference signal bitmap.
 69. A computer program productcomprising a non-transitory computer-readable memory bearing computerprogram code embodied therein for use with a computer, the computerprogram code comprising: code for receiving information indicating oneor more sets of reference signal patterns from a first transmissionpoint, wherein the one or more sets of reference signal patternscomprise one or more muting reference signal patterns that have zerotransmit power for certain frames of transmissions by the firsttransmission point; code for measuring the channel quality for theindicated one or more sets of reference signal patterns using the one ormore muting reference signal patterns; and code for reportingindications of the measured channel quality for the indicated one ormore sets of reference signal patterns to the first transmission point.70. The computer program product of claim 69, wherein measuring thechannel quality is performed in response to signaling from the firsttransmission point indicating the indicated one or more sets ofreference signal patterns are to be measured for signal quality.
 71. Anapparatus comprising: one or more processors; and one or more memoriesincluding computer program code, the one or more memories and thecomputer program code configured, with the one or more processors, tocause the apparatus to perform at least the following: transmittinginformation indicating one or more sets of reference signal patternsfrom a first transmission point to a user equipment, wherein the one ormore sets of reference signal patterns comprise one or more mutingreference signal patterns that have zero transmit power for certainframes of transmissions by the first transmission point; and receivingfrom the user equipment indications of channel quality for the indicatedone or more sets of reference signal patterns that are measured usingthe one or more muting reference signal patterns.
 72. The apparatus ofclaim 71, wherein the at least one memory and the computer program codeare further configured, with the at least one processor, to cause theapparatus to perform at least the following: determining a userequipment specific set of reference signal patterns the user equipmentshould measure; and signaling an indication to the user equipment of thedetermined user equipment specific set of reference signal patterns theuser equipment should measure.
 73. The apparatus of claim 71, whereinthe at least one memory and the computer program code are furtherconfigured, with the at least one processor, to cause the apparatus toperform at least the following: determining channel quality informationto be provided by the user equipment to the first transmission point forthe measured channel quality; and signaling indications of thedetermined channel quality information to the user equipment.
 74. Theapparatus of claim 71, wherein the at least one memory and the computerprogram code are further configured, with the at least one processor, tocause the apparatus to perform at least the following: sending a channelstate information-reference signals report request message to the userequipment to request the user equipment to measure the channel quality.75. The apparatus of claim 71, wherein the receiving comprises receivinga channel state information-reference signals quality report message.76. The apparatus of claim 71, wherein: the first transmission point isin a cell; the one or more other transmission points are a plurality ofother transmission points; at least one of the plurality of othertransmission points is in the cell; and at least an additional one ofthe plurality of other transmission points are in one or more neighborcells.
 77. The apparatus of claim 71, wherein the at least one memoryand the computer program code are further configured, with the at leastone processor, to cause the apparatus to perform at least the following:prior to receiving, signaling the user equipment an indication the oneor more sets of reference signal patterns are to be measured for signalquality.
 78. A method comprising: transmitting information indicatingone or more sets of reference signal patterns from a first transmissionpoint to a user equipment, wherein the one or more sets of referencesignal patterns comprise one or more muting reference signal patternsthat have zero transmit power for certain frames of transmissions by thefirst transmission point; and receiving from the user equipmentindications of channel quality for the indicated one or more sets ofreference signal patterns that are measured using the one or more mutingreference signal patterns.
 79. A computer program product comprising anon-transitory computer-readable memory bearing computer program codeembodied therein for use with a computer, the computer program codecomprising: code for transmitting information indicating one or moresets of reference signal patterns from a first transmission point to auser equipment, wherein the one or more sets of reference signalpatterns comprise one or more muting reference signal patterns that havezero transmit power for certain frames of transmissions by the firsttransmission point; and code for receiving from the user equipmentindications of channel quality for the indicated one or more sets ofreference signal patterns that are measured using the one or more mutingreference signal patterns.